In bidirectional communication lines, if either the supply voltage or ground is disconnected while a device is driving a communication line, the device potentially can stay in an active state. This results in a fault condition. A secondary power path via signaling pins enables continued operation, but this can consume high currents and risks bringing down all communications. Additionally, oscillation between high and low loading on the host signal pad can ensue, damaging pad circuitry. A worst-case scenario can occur if a fault occurs in a system in which multiple devices are connected to the communication line.
Conventional solutions apply capacitor filtering on the voltage supply line to filter oscillation, but during a supply disconnect fault condition there is no direct current supply for the device, with only the capacitor to supply current. Applications are therefore limited based on how much current the capacitor can provide before device overloading is triggered. Further, the capacitor requires additional area, which is typically at a premium.
Therefore, there is a need for improved communication line driver protection systems and methods.